MPLS Working Group I. Busi (Ed)
Internet Draft Alcatel-Lucent
Intended status: Informational
B. Niven-Jenkins (Ed)
BT
Expires: September 2009 March 9, 2009
MPLS-TP OAM Framework and Overview
draft-busi-mpls-tp-oam-framework-01.txt
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Abstract
Multi-Protocol Label Switching (MPLS) Transport Profile (MPLS-TP) is
based on a profile of the MPLS and pseudowire (PW) procedures as
specified in the MPLS Traffic Engineering (MPLS-TE), pseudowire (PW)
and multi-segment PW (MS-PW) architectures complemented with
additional Operations, Administration and Maintenance (OAM)
procedures for fault, performance and protection-switching management
for packet transport applications that do not rely on the presence of
a control plane.
This document provides a framework that supports a comprehensive set
of OAM procedures that fulfills the MPLS-TP OAM requirements [11].
Table of Contents
1. Introduction.................................................3
1.1. Contributing Authors....................................3
2. Conventions used in this document............................3
2.1. Terminology.............................................4
2.2. Definitions.............................................4
3. Functional Components........................................5
3.1. Maintenance Entity......................................6
3.2. Maintenance End Points (MEPs)...........................7
3.3. Maintenance Intermediate Points (MIPs)..................8
3.4. Server MEPs.............................................9
4. Reference Model..............................................9
4.1. MPLS-TP Section Monitoring.............................12
4.2. MPLS-TP LSP End-to-End Monitoring......................13
4.3. MPLS-TP LSP Tandem Connection Monitoring...............14
4.4. MPLS-TP PW Monitoring..................................15
4.5. MPLS-TP MS-PW Tandem Connection Monitoring.............16
5. OAM Functions for pro-active monitoring.....................17
5.1. Continuity Check and Connectivity Verification.........17
5.1.1. Applications for proactive CC & CV function.......19
5.2. Remote Defect Indication...............................20
5.2.1. Configuration considerations......................20
5.2.2. Applications for Remote Defect Indication.........20
5.3. Alarm Suppression......................................21
5.4. Lock Indication........................................21
5.5. Packet Loss Measurement................................21
5.6. Client Signal Fail.....................................22
6. OAM Functions for on-demand monitoring......................22
6.1. Continuity Check and Connectivity Verification.........22
6.1.1. Configuration considerations......................23
6.2. Packet Loss Measurement................................23
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6.3. Diagnostic Test........................................23
6.4. Trace routing..........................................23
6.5. Packet Delay Measurement...............................23
7. OAM Protocols Overview......................................23
8. Security Considerations.....................................23
9. IANA Considerations.........................................24
10. Acknowledgments............................................24
11. References.................................................25
11.1. Normative References..................................25
11.2. Informative References................................25
1. Introduction
As noted in the MPLS-TP framework [8], the overall architecture of
MPLS-TP is based on a profile of the MPLS-TE and (MS-)PW
architectures defined in RFC 3031 [2], RFC 3985 [5] and [6]
complemented with additional OAM procedures for fault, performance
and protection-switching management for packet transport applications
that do not rely on the presence of a control plane.
In line with [12], existing MPLS OAM mechanisms will be used wherever
possible and extensions or new OAM mechanisms will be defined only
where existing mechanisms are not sufficient to meet the
requirements.
The MPLS-TP OAM framework provides a comprehensive set of OAM
procedures while satisfying the MPLS-TP OAM requirements [11]. In
this regard, it is similar to existing SONET/SDH and OTH OAM
mechanisms (e.g. [13]).
[Editor's note - Sections 1, 2 and 3 of this version of the draft
have been already reviewed by MEAD. Further revisions will be
undertaken and the outcome of these revisions included in the next
version of this draft]
1.1. Contributing Authors
Italo Busi, Ben Niven-Jenkins, Annamaria Fulignoli, Enrique
Hernandez-Valencia, Lieven Levrau, Dinesh Mohan, Vincenzo Sestito,
Nurit Sprecher, Huub van Helvoort, Martin Vigoureux, Yaacov
Weingarten, Rolf Winter
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [1].
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2.1. Terminology
LME LSP Maintenance Entity
LTCME LSP Tandem Connection Maintenance Entity
[Editor's note - Difference or similarity between tandem connection
monitoring (TCM)_and Path Segment Tunnel (PST) need to be defined and
agreed]
ME Maintenance Entity
[Editor's note - There is a need to define whether to support OAM on
p2mp transport path there is a need to introduce the MEG concept]
MEP Maintenance End Point
MIP Maintenance Intermediate Point
PME PW Maintenance Entity
PTCME PW Tandem Connection Maintenance Entity
SME Section Maintenance Entity
2.2. Definitions
Concatenated Segment: see [10]
Co-routed bidirectional path: see [10]
Layer network: see [10]
Section: see [10]
OAM flow: An OAM flow is a traffic flow between a pair of MEPs or a
MEP and a MIP that is used to monitor a ME [Editor's note - a MEG
depending on what we decide for this point]. The OAM flow is
associated to a unique ME and contains the OAM monitoring, signalling
and notification messages necessary to monitor and maintain that ME.
The exact mix of message types in an OAM flow will be dependent on
the technology being monitored and the exact deployment scenario of
that technology (e.g. some deployments may proactively monitor the
connectivity of all transport paths whereas other deployments may
only reactively monitor transport paths)
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MIP: A MIP terminates and processes OAM messages and generates OAM
messages in reaction to received OAM messages.
MEP Source: A MEP acts as MEP source for the OAM flow that it
originates and inserts into its associated ME.
MEP Sink: A MEP acts as a MEP sink for the OAM flow that it
terminates and processes from it associated ME.
OAM Message: An OAM information element that performs some OAM
functionality (e.g. continuity and connectivity verification)
OAM Packet: A packet that carries one or more OAM messages (i.e. OAM
information elements).
Path: See Transport Path
Segment: see [10]
Sublayer: see [10]
Tandem Connection: see [10]
Transport Path: see [10]
Unidirectional path: see [10]
3. Functional Components
MPLS defines the use of Label Switched Paths (LSPs) and Pseudowires
(PWs)([2], [5] and [7]) that are used to connect service end points.
MPLS-TP builds on this framework the need to transport service
traffic, based on certain performance and quality measurements. In
order to verify and maintain these performance and quality
measurements, we need to use the OAM functionality not only on an
transport paths (e.g. LSP or MS-PW), but also on arbitrary parts of
transport paths, defined as Tandem Connections in [10], between any
two arbitrary points along a path.
MPLS-TP OAM operates in the context of Maintenance Entities (MEs).
A Maintenance Entity can be viewed as the association of two (or
more) Maintenance End Points (MEPs), see below. The MEPs that form an
ME are configured and managed to limit the scope of an OAM flow
within the ME the MEPs belong to.
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Each MEP resides at the boundaries of the ME that they are part of.
An ME may also include a set of zero or more Maintenance Intermediate
Points (MIPs), which reside within the Maintenance Entity, between
the MEPs.
A MEP is capable of initiating and terminating OAM messages for fault
management and performance monitoring.
A MIP is capable of terminating OAM messages but it generates OAM
messages only in reaction to received OAM messages.
This functional model defines the relationships between all OAM
entities from a maintenance perspective, to allow each Maintenance
Entity to monitor and manage the layer network under its
responsibility and easily localize problems.
MEPs and MIPs are associated with a particular Maintenance Entity.
When a control plane is not present, the management plane configures
MEPs and MIPs. Otherwise they can be configured either by the
management plane or by the control plane.
[Editor's note - Need to align the two paragraphs above with the
outcome of the on-going discussion on the mailing list regarding the
usage of control plane to configure OAM]
3.1. Maintenance Entity
A Maintenance Entity can be viewed as the association of two (or
more) Maintenance End Points (MEPs). An example of an ME with more
than two MEPs is a point-to-multipoint ME monitoring a point-to-
multipoint transport path (or point-to-multipoint tandem connection).
The MEPs that form an ME should be configured and managed to limit
the OAM responsibilities of an OAM flow within a network or sub-
network, or a transport path or segment, in the specific layer
network that is being monitored and managed. Any maintenance point in
between MEPs is a Maintenance Intermediate Points (MIP).
A Maintenance Entity may be defined to monitor and manage
unidirectional point-to-point or point-to-multipoint transport paths
or tandem connections, or co-routed bidirectional point-to-point
transport paths and tandem connections in an MPLS-TP layer network.
MPLS-TP OAM functions are designed to be applied either on an end-to-
end basis, e.g., between the LERs of a given LSP or T-PEs of a given
PW, or on a per tandem connection basis, e.g., between any LER/LSR of
a given LSP or any T-PE/S-PE of a given PW.
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The end points of a tandem connection are MEPs because the tandem
connection is by definition a Maintenance Entity.
Therefore, in the context of MPLS-TP LSP or PW Maintenance Entity
(defined below) LERs and T-PEs can be MEPs while LSRs and S-PEs may
be MIPs. In the case of Tandem Connection Maintenance Entity (defined
below), LSRs and S-PEs can be either MEPs or MIPs.
The following properties apply to all MPLS-TP MEs:
o They can be nested but not overlapped, e.g. a ME may cover a
segment or a concatenated segment of another ME, and may also
include the forwarding engine(s) of the node(s) at the edge(s) of
the segment or concatenated segment, but all its MEPs and MIPs are
no longer part of the encompassing ME. It is possible that MEPs of
nested MEs reside on a single node.
o Each OAM flow is associated with a single Maintenance Entity.
o OAM packets are subject to the same forwarding treatment (e.g.
fate share) as the data traffic, but they can be distinguished
from the data traffic using the GAL and ACH constructs [9] for LSP
and the ACH construct [6] [9] for (MS-)PW.
3.2. Maintenance End Points (MEPs)
Maintenance End Points (MEPs) are the end points of a ME. MEPs are
responsible for activating and controlling all of the OAM
functionality for the ME. A MEP may initiate an OAM packet to be
transferred to its corresponding MEP, or to an intermediate MIP that
is part of the ME.
MEPs prevent OAM packets corresponding to a ME from leaking outside
that ME:
o A MEP sink terminates all the OAM packets that it receives
corresponding to its ME and does not forward them further along
the path. If the pro-active CC&CV OAM tool detects an unintended
connectivity, all traffic on the path is blocked (i.e. all
received packets are dropped, including user-data packets).
o A MEP source tunnels all the OAM packets that it receives,
upstream from the associated ME, via label stacking. These packets
are not processed within the ME as they belong to another ME.
[Editor's - Need to rephrase the bullet above to clarify what it
actually means]
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MPLS-TP MEP notifies a fault indication to the MPLS-TP client layer
network.
A MEP of a tandem connection is not necessarily coincident with the
termination of the MPLS-TP transport path (LSP or PW), though it can
monitor it for failures or performance degradation (e.g. count
packets) within the boundary of the tandem connection.
[Editor's note - The MEP of a TCM monitors the transport paths'
connectivity within the scope of the TCM. This means that failures or
performance degradations within the TCM are detected by the TCM MEP
while failures or performance degradations outside the TCM are not
detected by the TCM MEP.
Is the text above sufficient to explain this concept?]
A MEP of an MPLS-TP transport path coincides with transport path
termination and monitors it for failures or performance degradation
on an end-to-end scope (e.g. count packets). Note that both MEP
source and MEP sink coincide with transport paths' source and sink
terminations.[Editor's note - Add some text regarding MEP
identification]
3.3. Maintenance Intermediate Points (MIPs)
A Maintenance Intermediate Point (MIP) is a point between the two
MEPs in an ME that is capable of reacting to some OAM packets and
forwarding all the other OAM packets while ensuring fate sharing with
data plane packets. A MIP belongs to only one ME.
A MIP does not initiate unsolicited OAM packets, but may be addressed
by OAM packets initiated by one of the MEPs of the ME. A MIP can
generate OAM packets only in response to OAM packets that are sent on
the ME it belongs to.
[Editor's note - It is needed to describe about how this is achieved
(e.g. TTL expiry). Is this description in the scope of this
document?]
MIPs are unaware of any OAM flows running between MEPs or between
MEPs and other MIPs. MIPs can only receive and process OAM packets
addressed to the MIP itself.
A MIP takes no action on the MPLS-TP transport path.
[Editor's note - Add some text regarding MIP identification]
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3.4. Server MEPs
A server MEP is a MEP of an ME that is either:
o defined in a layer network below the MPLS-TP layer network being
referenced, or
o defined in a sub-layer of the MPLS-TP layer network that is below
the sub-layer being referenced.
A server MEP coincides with either a MIP or a MEP in the client
(MPLS-TP) layer network.
For example, a server MEP can be either:
o A termination point of a physical link (e.g. 802.3), an SDH VC or
OTH ODU for the MPLS-TP Section layer network, defined in section
4.1. ;
o An MPLS-TP Section MEP for MPLS-TP LSPs, defined in section 4.2. ;
o An MPLS-TP LSP MEP for MPLS-TP PWs, defined in section 4.4. ;
o An MPLS-TP LSP Tandem Connection MEP for higher-level LTCMEs,
defined in section 4.3. ;
o An MPLS-TP PW Tandem Connection MEP for higher-level PTCMEs,
defined in section 4.5.
The server MEP can run appropriate OAM functions for fault detection
within the server (sub-)layer network, and notifies a fault
indication to the MPLS-TP layer network.
4. Reference Model
The reference model for the MPLS-TP framework builds upon the concept
of an ME, and its associated MEPs and MIPs, to support the functional
requirements specified in [11].
The following MPLS-TP MEs are specified in this document:
o A Section Maintenance Entity (SME), allowing monitoring and
management of MPLS-TP Sections (between MPLS LSRs).
o A LSP Maintenance Entity (LME), allowing monitoring and management
of an end-to-end LSP (between LERs).
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o A PW Maintenance Entity (PME), allowing monitoring and management
of an end-to-end SS/MS-PWs (between T-PEs).
o An LSP Tandem Connection Maintenance Entity (LTCME), allowing
monitoring and management of an LSP Tandem Connection between any
LER/LSR along the LSP.
o A MS-PW Tandem Connection Maintenance Entity (PTCME), allows
monitoring and management of a SS/MS-PW Tandem Connection between
any T-PE/S-PE along the (MS-)PW.
The MEs specified in this MPLS-TP framework are compliant with the
architecture framework for MPLS MS-PWs [7] and MPLS LSPs [2].
Hierarchical LSPs are also supported. In this case, each LSP Tunnel
in the hierarchy is a different sub-layer network that can be
monitored, independently from higher and lower level LSP tunnels in
the hierarchy, end-to-end (from LER to LER) by an LME. Tandem
Connection monitoring via LTCME are applicable on each LSP Tunnel in
the hierarchy.
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Native |<-------------------- PW15 --------------------->| Native
Layer | | Layer
Service | |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| | Service
(AC1) V V LSP V V LSP V V LSP V V (AC2)
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| | | |=========| |=========| |=========| | | |
| CE1|--------|........PW1........|...PW3...|........PW5........|-------|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
. . . .
| | | |
|<- Subnetwork A ->| |<- Subnetwork Z ->|
.------------------- PW15 PME -------------------.
.---- PW1 PTCME ----. .---- PW5 PTCME ----.
.---------. .---------.
PSN13 LME PSNXZ LME
.---. .---. .---------. .---. .---.
Sec12 Sec23 Sec3X SecXY SecYZ
SME SME SME SME SME
TPE1: Terminating Provider Edge 1 SPE2: Switching Provider Edge 3
TPEX: Terminating Provider Edge X SPEZ: Switching Provider Edge Z
.---. ME . MEP ==== LSP .... PW
Figure 1 Reference Model for the MPLS-TP OAM Framework
Figure 1 depicts a high-level reference model for the MPLS-TP OAM
framework. The figure depicts portions of two MPLS-TP enabled
subnetworks, Subnetwork A and Subnetwork Z. In Subnetwork A, LSR 1 is
adjacent to LSR 2 via the MPLS Section Sec12 and LSR2 is adjacent to
LSR3 via the MPLS Section Sec23. Similarly, In Subnetwork Z, LSR X is
adjacent to LSR Y via the MPLS Section SecXY and LSR Y is adjacent to
LSR Z via the MPLS Section SecYZ. In addition, LSR 3 is adjacent to
LSR X via the MPLS Section 3X.
Figure 1 also shows a bi-directional MS-PW (PW15) between AC1 on LSR
1 (TPE1) and AC2 on LSR Z (TPEZ). The MS-PW consists of 3 bi-
directional PW Segments: 1) PW Segment 1 (PW1) between LSR 1 (TPE1)
and LSR 3 (SPE3) via the bi-directional PSN13 LSP, 2) PW Segment 3
(PW3) between LSR 3 (SPE3) and LSR X (SPEX), and 3) PW Segment 5
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(PW5) between LSR X (SPEX) and LSR Z (TPEZ) via the bi-directional
PSNXZ LSP.
The MPLS-TP OAM procedures that apply to an instance of a given ME
are expected to operate independently from procedures on other
instances of the same ME and certainly of other MEs. Yet, this does
not preclude that multiple MEs may be affected simultaneously by the
same network condition, for example, a fiber cut event.
Note that there are no constrains imposed by this OAM framework on
the number, or type, of MEs that may be instantiated a particular
node. In particular, when looking at Figure 1, it should be possible
to configure one or more MEPs from the same node if each MEP shares
the same node.
The subsections below define the MEs specified in this MPLS-TP OAM
architecture framework document. Unless otherwise stated, all
references to subnetworks, LSRs, MPLS Sections, LSP, pseudowires and
MEs in this Section are made in relation to those shown in Figure 1.
[Editor's note - Do we need to use the "Subnetwork" definition? For
the scope of this description, I think we could use "OAM domain" or
"administrative domain"]
4.1. MPLS-TP Section Monitoring
An MPLS-TP Section ME (SME) is an MPLS-TP maintenance entity intended
to monitor the forwarding behaviour of an MPLS Section as defined in
[10]. An SME may be configured on any MPLS section. SME OAM packets
fate share with the user data packets sent over the monitored MPLS
Section.
An SME is intended to be deployed for applications where it is
preferable to monitor the link between the topologically adjacent
MPLS (and MPLS-TP enabled) LSRs rather than monitoring the individual
LSP or PW segments traversing the MPLS Section and the server layer
technology does not provide adequate OAM capabilities.
A representative application is collecting link-level PM statistics
at the node-to-node interfaces (NNI) in MPLS-TP sub-network domains.
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|<-------------------- PW15 --------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
V V LSP V V LSP V V LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| | AC1 | |=========| |=========| |=========| | AC2 | |
| CE1|--------|........PW1........|...PW3...|........PW5........|-------|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
.--. .--. .--------. .--. .--.
Sec12 SME Sec23 SME Sec3X SME SecXY SME SecYZ SME
Figure 2 Reference Example of MPLS-TP Section MEs (SME)
Figure 2 shows 5 Section MEs configured in the path between AC1 and
AC2: 1) Sec12 ME associated with the MPLS Section between LSR 1 and
LSR 2, 2) Sec23 ME associated with the MPLS Section between LSR 2 and
LSR 3, 3) Sec3X ME associated with the MPLS Section between LSR 3 and
LSR X, 4) SecXY ME associated with the MPLS Section between LSR X and
LSR Y, and 5) SecYZ ME associated with the MPLS Section between LSR Y
and LSR Z.
4.2. MPLS-TP LSP End-to-End Monitoring
An MPLS-TP LSP ME (LME) is an MPLS-TP maintenance entity intended to
monitor the forwarding behaviour of an end-to-end LSP between two
(e.g., a point-to-point LSP) or more (e.g., a point-to-multipoint
LSP) LERs. An LME may be configured on any MPLS LSP. LME OAM packets
fate share with user data packets sent over the monitored MPLS-TP
LSP.
An LME is intended to be deployed in scenarios where it is desirable
to monitor the forwarding behaviour of an entire LSP between its
LERs, rather than, say, monitoring individual PWs. A representative
application is collecting PM statistics of PSN LSP that is being used
to provide a "tunnelling services" for a number of other LSPs.
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|<-------------------- PW15 --------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
V V LSP V V LSP V V LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| | AC1 | |=========| |=========| |=========| | AC2 | |
| CE1|--------|........PW1........|...PW3...|........PW5........|-------|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
.---------. .---------.
PSN13 LME PSNXZ LME
Figure 3 Examples of MPLS-TP LSP MEs (LME)
Figure 3 depicts 2 LMEs configured in the path between AC1 and AC2:
1) the PSN13 LME between LER 1 and LER 3, and 2) the PSNXZ LME
between LER X and LER Y. Note that the presence of a PSN3X LME in
such a configuration is optional, hence, not precluded by this
framework. For instance, the SPs may prefer to monitor the MPLS-TP
Section between the two LSRs rather than the individual LSPs.
4.3. MPLS-TP LSP Tandem Connection Monitoring
An MPLS-TP LSP Tandem Connection Monitoring ME (LTCME) is an MPLS-TP
maintenance entity intended to monitor the forwarding behaviour of an
LSP tandem connection between a given pair of LSRs. Multiple LTCMEs
MAY BE configured on any LSP. The LSR may or may not be immediately
adjacent at the MPLS-TP layer. LTCME OAM packets fate share with the
user data packets sent over the monitored LSP segment.
A LTCME can be defined between the following entities:
o LER and any LSR of a given LSP.
o Any two LSRs of a given LSP.
An LTCME is intended to be deployed in scenarios where it is
preferable to monitor the behaviour of a part of an LSP rather than
the entire LSP itself. A representative application is when there is
a need to monitor a part of an LSP that extends beyond the
administrative boundaries of an MPLS-TP enabled administrative
domain.
Note that LTCMEs are equally applicable to hierarchical LSPs.
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|<--------------------- PW15 -------------------->|
| |
| |<--------------PSN1Z LSP-------------->| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
V V S-LSP V V S-LSP V V S-LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ | PE1| | | | PB3| | PBX| | | | PEZ| +----+
| | AC1 | |=======================================| | AC2 | |
| CE1|--------|......................PW15.......................|-------|CE2 |
| | | |=======================================| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
.---------. .---------.
PSN13 LTCME PSNXZ LTCME
.---------------------------------------.
PSN1Z LME
PB: Provider Border LSR
Figure 4 MPLS-TP LSP Tandem Connection Monitoring ME (LTCME)
Figure 4 depicts a variation of the reference model in Figure 1 where
there is an end-to-end PSN LSP (PSN1Z LSP) between PE1 and PEZ. PSN1Z
LSP consists of, at least, three stitched LSP Segments: PSN13, PSN3X
and PSNXZ. In this scenario there are two separate LTCMEs configured
to monitor the forwarding behaviour of the PSN1Z LSP: 1) a LTCME
monitoring the PSN13 LSP Segment on Subnetwork 123 (PSN13 LTCME), and
2) a LTCME monitoring the PSNXZ LSP Segment on Subnetwork XYZ (PSNXZ
LTCME).
It is worth noticing that LTCMEs can coexist with the LME monitoring
the end-to-end LSP and that LTCME MEPs and LME MEPs can be coincident
in the same node (e.g. PE1 node supports both the PSN1Z LME MEP and
the PSN13 LTCME MEP).
4.4. MPLS-TP PW Monitoring
An MPLS-TP PW ME (PME) is an MPLS-TP maintenance entity intended to
monitor the end-to-end forwarding behaviour of a SS-PW or MS-PW
between a pair of T-PEs. A PME MAY be configured on any SS-PW or MS-
PW. PME OAM packets fate share with the user data packets sent over
the monitored PW.
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A PME is intended to be deployed in scenarios where it is desirable
to monitor the forwarding behaviour of an entire PW between a pair of
MPLS-TP enabled T-PEs rather than monitoring the LSP aggregating
multiple PWs between PEs. A representative application is on either
SS-PW or MS-PW used to emulate traffic for which an SLA with QoS
commitments may apply (e.g., an emulated DS1/E1 or the emulated CBR
connection of an ATM VCC/VPC).
|<-------------------- PW15 --------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
V V LSP V V LSP V V LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| | AC1 | |=========| |=========| |=========| | AC2 | |
| CE1|--------|........PW1........|...PW3...|........PW5........|-------|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
.---------------------PW15 PME--------------------.
Figure 5 MPLS-TP PW ME (PME)
Figure 5 depicts a MS-PW (PW15) consisting of three segments: PW1,
PW3 and PW5 and its associated end-to-end PME (PW15 PME).
4.5. MPLS-TP MS-PW Tandem Connection Monitoring
An MPLS-TP MS-PW Tandem Connection Monitoring ME (PTCME) is an MPLS-
TP maintenance entity intended to monitor the forwarding behaviour of
an MS-PW tandem connection between a given pair of PEs. Multiple
PTCMEs MAY be configured on any MS-PW. The PEs may or may not be
immediately adjacent at the MS-PW layer. PTCME OAM packets fate share
with the user data packets sent over the monitored MS-PW Segment.
A PTCME can be defined between the following entities:
o T-PE and any S-PE of a given MS-PW
o Any two S-PEs of a given MS-PW. It can span several PW segments.
A PTCME is intended to be deployed in scenarios where it is
preferable to monitor the behaviour of a part of a MS-PW rather than
the entire end-to-end PW itself. A representative application is to
collect PM statistics for the MS-PW Segment within a given network
domain of an inter-domain PW.
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|<-------------------- PW15 --------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
V V LSP V V LSP V V LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| | AC1 | |=========| |=========| |=========| | AC2 | |
| CE1|--------|........PW1........|...PW3...|........PW5........|-------|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
.---- PW1 PTCME ----. .---- PW5 PTCME ----.
.---------------------PW15 PME--------------------.
Figure 6 MPLS-TP MS-PW Tandem Connection Monitoring (PTCME)
Figure 6 depicts the same MS-PW (PW15) between AC1 and AC2 as in
Figure 5. In this scenario there are two separate PTCMEs configured
to monitor the forwarding behaviour of PW15: 1) a PTCME monitoring
the PW1 MS-PW Segment on Subnetwork 123 (PW1 PTCME), and 2) a PTCME
monitoring the PW4 MS-PW Segment on Subnetwork XYZ with (PW5 PTCME).
It is worth noticing that PTCMEs can coexist with the PME monitoring
the end-to-end MS-PW and that PTCME MEPs and PME MEPs can be
coincident in the same node (e.g. TPE1 node supports both the PW15
PME MEP and the PW1 PTCME MEP).
5. OAM Functions for pro-active monitoring
5.1. Continuity Check and Connectivity Verification
Proactive Continuity and Connectivity Verification (CC & CV) function
is used to detect loss of continuity (LOC), unexpected connectivity
between two MEs (e.g. mismerging or misconnection) as well as
unexpected connectivity within the ME with an unexpected MEP.
Proactive CC & CV is based upon the generation of OAM pro-active
CC/CV packets, carrying a unique ME identifier, at a regular
configurable timing rate and the detection of LOC when these packets
do not arrive. If the received ME identifier does not match the
expected ME identifier, a connectivity defect has occurred. The
default CC/CV transmission periods are application dependent (see
section 5.1.1. )
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[Editor's Note - CC packets should be transmitted with the "minimum
loss-probability PHB". Is PHB configurable? If not, how the PHB for
CC is decided?]
For statically provisioned connections, the transmission period and
the ME identifier are statically configured at both MEPs. For
dynamically established connections, the transmission period and the
ME identifier are signaled via the control plane.
In a bidirectional point-to-point transport path, when a MEP is
enabled to generate pro-active CC/CV packets with a configured
transmission period, it also expects to receive pro-active CC/CV
packets from its peer MEP with the same transmission period. In a
unidirectional transport path (point-to-point or point-to-
multipoint), only the source MEP is enabled to generate packets with
CC/CV information. This MEP does not expect to receive any packets
with CC/CV information from its peer MEPs in the ME.
MIPs as well as intermediate nodes not supporting MPLS-TP OAM are
transparent to the pro-active CC/CV information and forward pro-
active CC/CV packets as regular data packets.
When CC & CV is enabled, a MEP periodically transmits pro-active
CC/CV packets with frequency of the configured transmission period.
When a MEP enabled to receive pro-active CC/CV packets
When CC & CV is enabled, a MEP detects loss of continuity (LOC)
defect with a peer MEP when it receives no pro-active CC/CV packets
from the peer MEP within the interval equal to 3.5 times the
transmission period.
When a pro-active CC/CV packet is received, a MEP is able to detect a
mis-connectivity defect (e.g. mismerge or misconnection) with another
ME when the received packet carries an incorrect ME identifier
If pro-active CC/CV packets are received with a transmission period
different than expected, CC/CV period mis-configuration defect is
detected.
[Editor's note - We need to understand whether a mechanism for auto-
negotiate the actual transmission period such that in case of period
mis-configuration the two MEPs converge on the slower speed is
required. It is anyway important to report to the operator the fact
that the negotiated speed mismatches the configured one. Do we need
to add some text to capture the capability to auto-negotiate the rate
between MEPs?]
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[Editor's note - Need to add the defect clearing conditions]
A receiving MEP notifies the equipment fault management process when
it detects the above defect conditions.
If a MEP detects an unexpected connectivity it MUST block all the
traffic (including also the user data packets) that it receives from
the misconnected connection.
It is worth noticing that the OAM requirements document [11]
recommends that CC-CV proactive monitoring is enabled on every ME in
order to reliably detect connectivity defects.
However, CC-CV proactive monitoring can be disabled by an operator on
a ME. In this case a dLOC can be a connectivity problem (e.g. a
misconnection with a connection where CC-CV proactive monitoring is
not enabled) and not necessarily a continuity problem, with a
consequent wrong traffic delivering.
For these reasons, the traffic block consequent action SHOULD be
applied even when a LOC condition occurs.
The activation of the traffic block consequent action should be
configurable (i.e. it should be possible to enable/disable the
consequent action) in case of LOC condition; that in order to
enable/disable the proactive CC-CV monitoring on a ME in a not
traffic affecting way.
5.1.1. Applications for proactive CC & CV function
CC & CV is applicable for fault management, performance monitoring,
or protection switching applications.
o Fault Management: default transmission period is 1s (i.e.
transmission rate of 1 packet/second)
o Performance Monitoring: default transmission period is 100ms (i.e.
transmission rate of 10 packets/second)
o Protection Switching: in order to achieve sub-50ms recovery time
the default transmission period is 3.33ms (i.e. transmission rate
of 300 packets/second) although a transmission period of 10ms can
also be used. In some cases, when a slower recovery time is
acceptable, it is also possible to relax the transmission period.
[Editor's note - We can turn this into something more formulaic.
Given a desired switching time of Xms, and a hardware switching time
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of Yms, and an OAM message propagation time of Zms, the transmission
period should be set to no greater than t = (X-Y-Z)/n assuming that
switchover will not be triggered until n protection switching
messages have failed to be received.]
5.2. Remote Defect Indication
The Remote Defect Indication (RDI) is an indicator that is
transmitted by a MEP to communicate to its peer MEPs that a signal
fail condition exists. RDI is only used for bidirectional
connections and is associated with proactive CC & CV packet
generation.
[Editor's note - Add more specific information about the signal fail
conditions reported by RDI.]
A MEP that has identified a signal fail related defect should include
the RDI in all pro-active CC/CV packets that it generates for the
duration of the signal fail condition existence.
A MEP that receives the packets with the RDI information should
determine that its peer MEP has encountered a defect condition
associated with a signal fail (i.e. detect an RDI defect).
MIPs should be transparent to the RDI indicator and transparently
forwards pro-active CC/CV packets that include the RDI indicator,
i.e. the MIP should not perform any actions nor examine the
indicator.
When the signal fail condition clears, the MEP should clear the RDI
indicator from subsequent transmission of pro-active CC/CV packets.
A MEP also clears the RDI defect upon reception of a pro-active CC/CV
packet from the source MEP with the RDI indicator cleared.
5.2.1. Configuration considerations
In order to support RDI indication, the RDI transmission rate and PHB
of the MEP should be configured as part of the CC & CV configuration.
5.2.2. Applications for Remote Defect Indication
RDI is applicable for the following applications:
o Single-ended fault management - A receiving MEP detects the RDI
defect condition, which when correlated with other defect
conditions in the receiving MEP may become a fault case.
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o Contribution to far-end performance monitoring - The indication of
the far-end defect condition is used as input to the performance
monitoring process.
5.3. Alarm Suppression
Alarm Indication Signal function (AIS) is used to suppress alarms
following detection of defect conditions at the server (sub) layer.
o Packets with AIS information can be issued at a MEP, including a
Server MEP, upon detecting signal fail conditions.
A server MEP is responsible for notifying the MPLS-TP layer network
MEP upon fault detection in the server layer network to which the
server MEP is associated.
Only Server MEPs can issue MPLS-TP packets with AIS information. Upon
detection of a signal fail condition the Server MEP can immediately
start transmitting packets with AIS information periodically. A
Server MEP continues to transmit periodic packets with AIS
information until the signal fail condition is cleared.
Upon receiving a packet with AIS information a MEP detects an AIS
defect condition and suppresses loss of continuity alarms associated
with all its peer MEPs. A MEP resumes loss of continuity alarm
generation upon detecting loss of continuity defect conditions in the
absence of AIS condition.
Specific configuration information required by a MEP to support AIS
transmission is the following:
o PHB - identifies the per-hop behaviour of packet with AIS
information.
A MIP is transparent to packets with AIS information and therefore
does not require any information to support AIS functionality.
5.4. Lock Indication
To be incorporated in a future revision of this document
5.5. Packet Loss Measurement
To be incorporated in a future revision of this document
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5.6. Client Signal Fail
To be incorporated in a future revision of this document
6. OAM Functions for on-demand monitoring
6.1. Continuity Check and Connectivity Verification
In order to preserve network resources, e.g. bandwidth, processing
time at switches, it may be preferable to not use continual pro-
active CC & CV. In order to perform fault management functions
network management may invoke periodic on-demand bursts of on-demand
CC/CV packets. Use of on-demand CC & CV is dependent on the
existence of a bi-directional connection ME.
An additional use of on-demand CC & CV would be to detect and locate
a problem of connectivity when a problem is suspected or known based
on other tools. In this case the functionality will be triggered by
the network management in response to a status signal or alarm
indication.
On-demand CC & CV is based upon generation of on-demand CC/CV packets
that should uniquely identify the ME that is being checked. The on-
demand functionality may be used to check either an entire ME (end-
to-end) or between a MEP to a specific MIP.
On-demand CC & CV may generate a one-time burst of on-demand CC/CV
packets, or be used to invoke periodic, non-continuous, bursts of on-
demand CC/CV packets. The number of packets generated in each burst
is configurable at the MEPs, and should take into account normal
packet-loss conditions.
When invoking a periodic check of the ME, the source MEP should issue
a burst of on-demand CC/CV packets that uniquely identifies the ME
being verified. The number of packets and their transmission rate
should be pre-configured and known to both the source MEP and the
target MEP or MIP. The source MEP should use the TTL field to
indicate the number of hops necessary, when targeting a MIP and use
the default value when performing an end-to-end check [IB => This is
quite generic for addressing packets to MIPs and MEPs so it is better
to move this text in section 2]. The target MEP/MIP shall return a
reply on-demand CC/CV packet for each packet received. If the
expected number of on-demand CC/CV reply packets is not received at
source MEP, a LOC state is detected.
[Editor's note - We need to add some text for the usage of on-demand
CC&CV with different packet sizes, e.g. to discover MTU problems.]
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When a connectivity problem is detected (e.g. via a pro-active CC&CV
OAM tool), on demand CC&CV tool can be used to check the path. The
series should check CC&CV from MEP to peer MEP on the path, and if a
fault is discovered, by lack of response, then additional checks may
be performed to each of the intermediate MIP to locate the fault.
6.1.1. Configuration considerations
For on-demand CC & CV the MEP should support configuration of number
of packets to be transmitted/received in each burst of transmissions
and the transmission rate should be either pre-configured or
negotiated between the different nodes.
In addition, when the CC & CV packet is used to check connectivity
toward a target MIP, the number of hops to reach the target MIP
should be configured.
The PHB of the on-demand CC/CV packets should be configured as well.
[Editor's note - We need to be better define the reason for such
configuration]
6.2. Packet Loss Measurement
To be incorporated in a future revision of this document
6.3. Diagnostic Test
To be incorporated in a future revision of this document
6.4. Trace routing
To be incorporated in a future revision of this document
6.5. Packet Delay Measurement
To be incorporated in a future revision of this document
7. OAM Protocols Overview
To be incorporated in a future revision of this document
8. Security Considerations
A number of security considerations important in the context of OAM
applications.
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OAM traffic can reveal sensitive information such as passwords,
performance data and details about e.g. the network topology. The
nature of OAM data therefore suggests to have some form of
authentication, authorization and encryption in place. This will
prevent unauthorized access to vital equipment and it will prevent
third parties from learning about sensitive information about the
transport network.
Mechanisms that the framework does not specify might be subject to
additional security considerations.
9. IANA Considerations
No new IANA considerations.
10. Acknowledgments
The authors would like to thank all members of the teams (the Joint
Working Team, the MPLS Interoperability Design Team in IETF and the
T-MPLS Ad Hoc Group in ITU-T) involved in the definition and
specification of MPLS Transport Profile.
This document was prepared using 2-Word-v2.0.template.dot.
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11. References
11.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997
[2] Rosen, E., Viswanathan, A., Callon, R., "Multiprotocol Label
Switching Architecture", RFC 3031, January 2001
[3] Rosen, E., et al., "MPLS Label Stack Encoding", RFC 3032,
January 2001
[4] Agarwal, P., Akyol, B., "Time To Live (TTL) Processing in
Multi-Protocol Label Switching (MPLS) Networks", RFC 3443,
January 2003
[5] Bryant, S., Pate, P., "Pseudo Wire Emulation Edge-to-Edge
(PWE3) Architecture", RFC 3985, March 2005
[6] Nadeau, T., Pignataro, S., "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007
[7] Bocci, M., Bryant, S., "An Architecture for Multi-Segment
Pseudo Wire Emulation Edge-to-Edge", draft-ietf-pwe3-ms-pw-
arch-05 (work in progress), September 2008
[8] Bocci, M., et al., " A Framework for MPLS in Transport
Networks", draft-ietf-mpls-tp-framework-00 (work in progress),
November 2008
[9] Vigoureux, M., Bocci, M., Swallow, G., Ward, D., Aggarwal, R.,
" MPLS Generic Associated Channel ", draft-ietf-mpls-tp-gach-
gal-02 (work in progress), February 2009
11.2. Informative References
[10] Niven-Jenkins, B., Brungard, D., Betts, M., sprecher, N., Ueno,
S., "MPLS-TP Requirements", draft-ietf-mpls-tp-requirements-04
(work in progress), February 2009
[11] Vigoureux, M., Betts, M., Ward, D., "Requirements for OAM in
MPLS Transport Networks", draft-ietf-mpls-tp-oam-requirements-
00 (work in progress), November 2008
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[12] Sprecher, N., Nadeau, T., van Helvoort, H., Weingarten, Y., "
MPLS-TP OAM Analysis", draft-sprecher-mpls-tp-oam-analysis-02
(work in progress), September 2008
[13] ITU-T Recommendation G.707/Y.1322 (01/07), " Network node
interface for the synchronous digital hierarchy (SDH)", 2007
Authors' Addresses
Italo Busi (Editor)
Alcatel-Lucent
Email: Italo.Busi@alcatel-lucent.it
Ben Niven-Jenkins (Editor)
BT
Email: benjamin.niven-jenkins@bt.com
Contributing Authors' Addresses
Annamaria Fulignoli
Ericsson
Email: annamaria.fulignoli@ericsson.com
Enrique Hernandez-Valencia
Alcatel-Lucent
Email: enrique@alcatel-lucent.com
Lieven Levrau
Alcatel-Lucent
Email: llevrau@alcatel-lucent.com
Dinesh Mohan
Nortel
Email: mohand@nortel.com
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Vincenzo Sestito
Alcatel-Lucent
Email: vincenzo.sestito@alcatel-lucent.it
Nurit Sprecher
Nokia Siemens Networks
Email: nurit.sprecher@nsn.com
Huub van Helvoort
Huawei Technologies
Email: hhelvoort@huawei.com
Martin Vigoureux
Alcatel-Lucent
Email: martin.vigoureux@alcatel-lucent.fr
Yaacov Weingarten
Nokia Siemens Networks
Email: yaacov.weingarten@nsn.com
Rolf Winter
NEC
Email: Rolf.Winter@nw.neclab.eu
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